Apparatus eor producing electrical oscillations



M. EA STHAM. APPARATUS FOR PRODUCING ELECTRICAL OSCILLATIONS. APPLICATION FILED DEC. 28, I914.

l 9 1 94, 1 5%. Patented Aug. 8, 1916.

' ceives and-gives up electrical energy during ran s'ra'rns PATENT moron.

MELVILLE EASTHAM, OF CAMBRIDGE, MASSACHUSETTS, ASSIGNOR TO GENERAL RADIO COMPANY, A CORPORATIONOF MASSACHUSETTS.

APPARATUS FOR PRODUCING ELECTRICAL OSCILLATIONS.

Application filed December 28, 1914. Serial No. 879,299.

To all whom it may concern:

Be it known that I, MELVILLE EASTHAM, a citizen of the United States, residing at Cambridge, in the county of Middlesex and State of Massachusetts, have invented cer-* tain new anduseful Improvements in Apparatus for Producing Electrical Oscillations; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

The present invention relates to apparatus for producing electrical oscillations and more particularly to such apparatus for use in wireless signa ing.

a One feature of the invention relates to the construction and coordination of an oscillatory circuit and an impulse circuit whereby the oscillations are produced by impact excitation. The oscillatory circuit,- which is preferably also the radiator circuit, is

closely coupled with an exciting or impulse circuit. The impulse circuit includes a condenser-and a discharge gap which is so constructed that, in conjunction with the rapid transfer of energy -from the impulse circuit to the oscillatory circuit due to the close cou pling between them, it serves to so rapidly quench the discharge that pure impact excitation, or a condition approximating pure impact excitation, is attained. The impulse circuit is not tuned to the oscillatory circuit but preferably has a natural time period considerably in excess of .thatof the oscillatory circuit.

Another feature of the invention relates to a reservoir circuit which-alternately rethe operation of the apparatus.

Still other features of the invention relate to certain combinations and arrangements of parts hereinafter described and particularly pointed out in the claims, the advantages' of which will be apparent to those skilled in the art.

In the drawings, Figure 1 is a diagrammatic View illustrating the preferred embodiment of the apparatus of the present invention, and Figs. 2 and 3 are diagrams indicating the relation between'the oscillations in the oscillatory circuit and the excitjng impulses in the impulse circuit.

Specification of Letters Patent.

Patented Aug. 8, 1916.

and then its mode of operation pointed out.

The oscillatory circuit, indicated generally by reference numeral 1, is an antenna or radiating circuit, and includes an aerial wire 2 which is grounded at 3. Included in the circuit 1 is anair-core auto-transformer 5. Closely coupled with the oscillatory circuit 1 by means of the auto-transformer 5, is a non-oscillatory exciting or impulse circuit 6. While the necessary close coupling is more easily got. by means of the direct cow pling of the auto-transformer, nevertheless, a transformer having separate primary and secondary coils might be employed. The impulse circuit is connected as shown,'to the auto-transformer so that it acts as a step-up transformer. The impulse circuit ,6 is a closed circuit including a discharge gap 7, a condenser 8, and an adjustable inductance 9. During the operation ofthe apparatus, the condenser 8 is alternately charged from the feeding circuit and discharged through the discharge gap 7. The discharge gap is a sectors of each disk alternately coincide with the sectors of the other disk and with the cutaway portions between the sectors. The speed of the disk 10 issuch that the raised sectors coincide with some audible frequency, for example five or six hundred coincidences per second. When the raised sectors of the gaps coincide, a succession or group of discharges from the condenser 8 takes place. When the sectors coincide with the cutaway portions of the op osite disk no discharge takes place. The e ect of the gap is to cause the sending of oscillations having an audible group frequency. An important feature of the gap and one which adapts it for use in the present apparatus is the efi'ective quenching of the discharge.

The two surfaces of the discharge gap are 105 other. As a consequence of this, the discharge does not form a localized persistent are, because thepoints at which the discharge takes place are continuously being separated by the movement of the surfaces and new and comparatively cool surfaces are presented. The disks are of comparatively heavy plates of copper which is a good heat conductor and the gap is constructed so as to readily radiate heat. The action of the gap in continuously presenting fresh and comparatively cool surfaces for the discharge in conjunction with its ready dissipation of heat, is important in that it permits comparatively large discharge currents to be employed in the impulse circuit so that a con'iparatively large amount of energy ma v be radiated from the antenna circuit.

The impulse circuit 6 is not tuned or in resonance with the oscillatory circuit 1. Instead, the impulse circuit 6 has a natural time period considerably greater than that of the oscillatory circuit 1. While it is preferable that the impulse circuit 6 have a natural period of about fifty per cent. greater than that of the oscillatory circuit 1, this is not necessary as the natural period of the impulse circuit 6 may vary from this preferred relation within comparatively wide limits. One of the advantages in having the impulse circuit untuned and out of resonance with the oscillatory circuit 1, resides in the fact that the impulse circuit 6 will not tend to resonate with the oscillatory circuit 1, and, therefore, the tendency of the oscillatory circuit 1 to react and retransfer energy to the impulse circuit is minimized. If the impulse circuit 6 had the same natural time period as the oscillatory circuit 1, a condition of resonance between them would result, and because of this, there would be an undesirable tendency for the impulse circuit 1 to re-transfer energy back to the impulse circuit 6. Because of the untuned relationship between the impulse circuit 6 and the oscillatory circuit 1, this undesirable tendency is counteracted. Another advantage in having the impulse circuit 6 out of tune with the oscillatory circuit 1 and of a greater natural time period, resides in the fact that there is produced in the impulse circuit 6 a current impulse or condenser discharge of greater wave length than the current waves in the oscillatory circuit. This impulse wave has a duration of over one half greater than the duration of a single alternation or half oscillation of the os-, cillatory current in the oscillatory circuit 1. The impulse wave, therefore, laps over about one and a half or more of the single alternations or half oscillations of the oscillatory current. As hereinafter pointed out, this impulse wave is such as to efiiciently transfer energy from the impulse circuit to'the oscillatory circuit.

. of time.

The condenser 8 is charged by means of a feeder circuit 15. The feeder circuit 15 includes a high tension direct current generator 16, having an electromotive force of about two thousand five hundred volts. The feeder circuit 15 includes choke coils 17 between the generator and its connection to the impulse circuit, for preventing the impulse circuit from reacting on the generator.

In the feeder circuit is included the sending key 18.

A reservoir circuit 20 is connected to the impulse circuit 6 for the purpose of storing energy during the time that the gap 7 is not discharging and delivering the energy to the impulse circuit when the gap 7 is discharging. The reservoir circuit 20 includes an inductance 21 and a condenser 22. The inductance 21 and the condenser 22 are so proportioned that the reservoir circuit 20 has a natural frequency approximating that of the group frequency caused by the rotary gap 7. The electrical dimensions of the circuit 20 are such that the circuit is enabled to absorb practically the full output of the generator 16 during the interval when no discharge takes place across the discharge gap 7. The reservoir circuit 20 thus permits the full output of the generator 16 to be utilized. The tuning of the reservoir circuit 20 to the group frequency of the discharge gap causes the energy to surge in and out of the reservoir circuit. 20, the energy surging into the reservoir circuit 20 while the raised sectors of the gap 7 are opposite the cutaway portions and; no discharge can take place in the gap 7, and surging out of the reservoir circuit to supplement the current delivered from the generator when the raised sectors of the gap 7 coincide and the group of condenser discharges takes place. The condenser 8 can receive energy and. transfer it through. the impulse circuit to the oscillatory circuit only during those intervals when the sectors of the gaps are in coincidence. The periods of coincidence occur many hundred times per second, so that the current absorbed by the condenser 8 is an intermittent current which is interrupted many hundred times a second. If the condenser 8 were connected directly across the direct current generator without the reservoir circuit 20, it would be necessary for the generator to furnish an interrupted current, each pulsation of which would have a duration of the order of about a thousandth of a second. The direct current generator, of course, has a considerable internal inductance, so that it would be impossible for the generator to build up its full current strength during this brief interval Consequently, without the reservoir circuit, only a fraction of the normal output of the generator would be available.

The operation of the apparatus is as follows: Assume the sending key 18 is closed and a signal is being sent. The generator 16 continuously supplies energy. During the intervals when the raised sectors of the gaps are opposite the cutaway portions of the opposite plate, no discharge takes place through the discharge gap 7 and the reservoir circuit 20 receives and stores energy. When the sectors of the gap come into coincidence, the condenser 8 is charged, partially directly from the generator 16 and partially from the reservoir circuit 20, and then discharged through the discharge gap 7. The frequency of the discharge across the discharge gap- 7 is determined by the length of time consumed for the condenser 8 to become charged to the potential necessary to break down the discharge gap. This time is dependent upon the capacity of the condenser 8 and the rate at which it is sup plied with current. This time can be varied by changing the relationship between the capacity of the condenser 8 and the rate at which itis charged. A number of con denser discharges takes place during each coincidence of the sectors of the gap. When the apparatus is adjusted to good Working condition, thecondenser discharge is non oscillatory and consists of a substantially uni-directional current impulse or wave. This current impulse begins when the potential across the discharge gap is suflicient to strike an arc and ceases when the potential across the discharge gap drops to a voltage sufiiciently low so that the arc is no longer maintained. The impulse circuit 6 is closely coupled with the oscillatory circuit 1, the coefiicient of coupling between the circuits being preferably more than fifty per cent. With one form of the apparatus, the most satisfactory results were obtained with a coeflicient of coupling of about sixty per cent. This coupling is closer than it has heretofore been the practice to employ in Wireless apparatus. This closer coupling is one of the essential factors in attaining impact excitation in the present apparatus. Because of the close coupling, practically all I of the energy in the impulse circuit 6 due to the discharge of the condenser is transferred to the oscillatory circuit 1 during a single current wave. This transfer of energy leaves so little electro-magnetic energy in the impulse circuit that the discharge gap is able to. then extinguish the arc. The general relation between the condenser discharge and the oscillations in the oscillatory circuit is indicated in' Figs. 2 and 3 of the draw'ngs. The current curves in Figs. 2 and 3 are plotted from Braun tube oscillograms which were taken injtesting the apparatus. The sources of error were such that the current curves are not plotted to exact scale. They do, however, serve to ship of the currents. It is to be understood, therefore, that Figs. 2 and 3 are diagrammatic in nature and that they do not purport to illustrate the exact form of the current impulses and oscillations or their exact phase relation, the purpose being to illustrate in an approximate way the relationship of the exciting impulse to the excited oscillation in order to more easily explain the present invention. In Fig. 2 is diagrammatically illustrated the relationship between the condenser discharge and the excited oscillations when the condenser is discharged at such a rate that a succeeding discharge impulse takes place before the previously excited wave train in the oscillatory circuit has died out. In Fig; 3 is diagrammatically indicated the relationship of the condenser discharge and the excited oscillations when the condenser is charged slow'ly enough so that the previously excited train of waves dies out before the succeeding condenser discharge.

In Fig. 2 the heavy lines 30 indicate the current impulse or condenser discharge in the impulse circuit 6 and the light line 31 indicates the oscillatory current in the oscillatory circuit 1. The positive maxima of the oscillatory current are indicated at 32, the negative maxima at 33, and the zero Values at 34. The oscillations in the oscillatory circuit are free oscillations and have of course substantially the same period as the natural time period of the oscillatory circuit. It will be noted that the current impulses 30 occur in a predetermined phase relationship with the oscillations. This is due to the fact that, as the condenser 8 is being charged from the feeder circuit, the oscillations in the oscillatory circuit 1 react on the impulse circuit 6 to impress ripples of electro-motive force across the discharge gap 7. These ripples of electro-moti ve force serve to trigger off the condenser discharge 30 in the predetermined phase relationship with the oscillations 31 which is indicated approximately in Fig. 2. The impulses 3O occur in such relationship to the, oscillations 31 that the condenser discharge impulses 30 reinforce and continue the already existing train of oscillations 31. The efiect of the impulse 30 is, therefore, not to appreciably change the phase relationship of the oscilthe oscillatory circuit intervenes between successive impulses in the impulse circuit, so that the num er of oscillations per unit of time is an integral multiple of the number of impulses.

In Fig. 3 the heavy line 40 indicates a current impulse or condenser discharge n the impulse circuit 6, and the light line 41 indicates the excited train of oscillations in the oscillatory circuit 1. The positive maxima of the oscillatory current are indicated at 42, the negative maxima at 43, and the zero values at 44. As shown in Fig. 3, the previously excited train of oscillations has died out before the impulse 40 takes place so that the train of excited oscillations 41 begins with the impulse 40.

As shown in both Figs. 2 and 3, the current impulses or condenser discharges indicated at and 40, have a considerably greater duration than the single alternations or half complete oscillations of the oscillatory current. As shown in Fig. 2, the condenser discharge 30 begins, due to the triggering, at a point between a' positive maximum 32 and the following zero value 34-of the oscillatory current 31, and continues until about the next succeeding positive maximum 32 of the oscillatory current.

Under this condition, the current impulse I or condenser discharge 30 has a duration .nearly twice that of the single alternations or waves of the oscillatory current 31. As shown in Fig. 3, the excited train of oscillations 41 begins at a zero point 44 which coincides with the beginning of the condenser discharge 40. The oscillations 41, of course, have approximately the natural time period of the oscillatory circuit 1. The current impulse or condenser discharge 40 laps over about one and one-half of the single alternations of the oscillatory current 41, terminating at about the first positive maximum 42. Thus, in this case, the current impulse 40 may be considered to have a wave length about one and one-half times as long as the wave length of the current in the oscillatory circuit.

The expression alternation is here used to define the single alternation-or current flow which takes place between two succeeding zero values of the oscillatory current. A complete oscillation is made up of two alternations, one alternation being positive and the other being negative.

The shape and duration of the exciting impulse or condenser discharges 30 and 40 is important for the transfer of energy from the impulse-circuit 6 to the oscillatory circuit 1. The electromotive force exerted by the impulse 30 or 40 on the oscillatory circuit 1 is expressed by the formula where M is the mutual inductance of the c1rcu1ts 6 and 1, i is the current impulse 1n the ir it and. t is the time. When the current i, is increasing to a positive maximum, the electromotive force is, of course,

negative and when the current 6 is decreastransfer energy from the impulse circuit 6 to the oscillatory circuit 1. I

Apparently there occurs one ormore brief periods during the impulse when the electromotive force is opposite in phase to the current in the oscillatory circuit, but the amount of energy which would be thus transferred back from the oscillatory to the impulse circuit when the induced electromotive force is opposite in phase to the oscillatory current is small compared with the energy transferred from the impulse to the.

oscillatory circuit when the induced electromotive force is in phase with the oscillatory current. When triggering takes place, as indicated in "Fig. 2, there is an initial trans fer of some energy from the oscillatory circuit 1 to the impulse circuit 6 in order to assist in breaking down the discharge gap. This energy is, however, immediately retransferred hack to the oscillatory circuit as soon as the induced electromotive force comes'into phase with the oscillatory current.

The exciting impulses are extinguished so quickly that the train of oscillations excited in the oscillatory circuit is a single period train of free oscillations, and thus the double period oscillations which are produced by current oscillations in two coupled oscillatory circuits and radiated as a double period- Substantially the entire energy transfer from the impulse to the oscillatory circuit takes place during a single current impulse or wave, and this wave has a duration considerably longer than the single waves or alternations of the oscillatory current which u it excites. In this respect the present ap paratus differs from the usual quenched gap type of apparatus in which a number of current waves take place in the exciting circuit and the current waves are of substantially the same wave length as the oscil' use is a spark ga .lations' which they excite. By virtue of this fact, a condition of practically pure impact excitation results in the present a paratus.

The present apparatus also di ers from the usual wireless apparatus, in that instead of having two circuits tuned or in resonance, the impulse circuit 6 of the present apparatus is decidedly out of tune with the oscillatory circuit 1, so that no resonance can take place between them. I

Still another distinction between the present apparatus and that of the usual construction resides in the fact that the coupling between the impulse and oscillatory circuits 6 and 1 respectively is much closer than that hitherto usual in commercial apparatus.

The present apparatus is particularly designed to operate under the heavy currents necessary for commercial wireless transmitting stations. One feature which apparently is of great importance, in making the present apparatus capable of commercial which is able to carry heavy currents. n the present .apparatus the spark gap is composed of two relatively moving good heat conducting metallic sur- "faces, in which the arc is prevented from continuing at any one place and in which the arc-heated surfaces are separated, and fresh and comparatively cool surfaces are continuously presented for subsequent discharges. It has been found that stationary gaps of the so called rectifying type, while operating under some particularly favorable conditions to permitunidirect'ional condenser discharges, are unsuited for commercial apparatus because they are incapable of operating under the necessary amounts of current. Apparently the discharge gap having relatively moving good heat conducting metallic .surfaces in combination with close coupling between the impulse and oscillatory circuits is necessary to render the apparatus capable of substantially ure impact excitation as hereinbefore described.

While I have explained the theory of the operation of the apparatus in some detail as it is at present understood by me, the invention resides in the apparatus and not in the theory, and in stating the probable theory it is not my intention to limit myself to such theor but rather to state it as the probable exp anation of the operation of my apparatus.

The present invention is not limited to the illustrated embodiment, but may be embodied in other constructions within the scope of the following claims.

I claim 1. An apparatus for producing electrical oscillations having, in combination, an oscillatory circuit, an impulse circuit coupled with the oscillatory circuit, the coeflicient of coupling between the two circuits being and a discharge gap comprising two relatively moving good heat conducting sur faces, and a feeder circuit for charging the condenser at such a rate that the condenser discharges. in the impulse circuit will. occur before the previously excited trains of oscillations in the oscillatory circuit dies down, said oscillations in the oscillatory circuitreacting on the impulse circuit and serving to trigger oif the condenser discharges -in a predetermined phase relation with the oscillations so as to reinforce and sustain the declining oscillations.

3. Apparatus for producing electrical oscillations having, in combination, an oscillatory circuit, and means for producing oscillations in the oscillatory circuit by impact excitation comprising an impulse circuit closely coupled with the oscillation circuit and including a condenser and a discharge gap liaving two relatively moving good heat conducting metallic surfaces, said spark gap in conjunction with the transfer of energy from the impulse circuit to the os cillatory circuit, due to the close coupling, serving to cause a substantially non-oscillatory condenser discharge in the impulse circuit, and a feeder circuit for charging the condenser.

4:. An apparatus for producing electrical oscillations having, in combination, an OS- cillatory circuit, an impulse circuit coupled with the oscillatory circuit, the co-efiicient of coupling between the two circuits being greater than fifty per cent., said impulse circuit including a condenser and a discharge gap comprising two relatively moving good heat conducting metallic surfaces, and a feeder circuit for charging the condenser.

5. Apparatus. for producing electrical oscillations having, in combination, an oscillatory circuit, and means for producing oscillations therein by impact excitation comprising an impulse circuit closely coupled with the oscillatory circuit and including a condenser and a discharge gap having relatively moving good heat conduct- 'ing metallic surfaces, said impulse circuit having a natural time period of at least considerably greater than the natural time period of the oscillatory circuit, said discharge gap taken in conjunction with the transfer of energy from the impulse circuit due to the close coupling between them,

ducting surfaces, and a feeder circuit for charging the condenser at such a rate that the condenser discharges in the impulse circuit Will occur before the previously excited trains of oscillations in the oscillatory circuit die down, said oscillations in the oscillatory circuit reacting on the impulse circuit and serving to trigger off the condenser d1scharges at a predetermined phase relation with the oscillations so as to reinforce and sustain the declining oscillations.

7. Apparatus for producing electrical oscillations having, in combination, an oscillatory circuit, and means for producing sustained oscillations therein by impact excita tion comprising an impulse circuit closely coupled with the oscillatory, circuit and including a condenser and a discharge gap having relatively moving good heat conducting metallic surfaces, said impulse circuit having a natural time period considerably greater than the natural time period of the oscillatory circuit, and a feeder circuit for charging the condenser at such a rate that the condenser discharges in the impulse circuit will occur before the previously excited trains of oscillations in the oscillatory circuit die down, said oscillations in the oscillatory circuit reacting on the impulse circuitand serving to trigger off the condenser discharges in a predetermined phase relationowith the oscillations so as to reinforce and sustain the declining oscillations.

8. Apparatus for producing electrical oscillations having, in combination, an oscillatory circuit, and means for producing sustained oscillations therein by impact excitation comprising an impulse circuit closely coupled with the oscillation circuit and including a condenser and a discharge ,gap having relatively moving good heat conducting metallic surfaces, said impulse circuit having a natural time period at least onehalf greater than the natural time period of the oscillatory circuit, said discharge gap taken in conjunction with the transfer of energy from the impulse to the oscillatory circuit due to the close coupling between them, serving to cause a substantially nonoscillatory condenser discharge in the impulse circuit of aduration greater than onehalf of the time of a complete current oscillation in theoscillatory circuit, and a feeder circuit for charging the condenser at such a rate that the condenser discharges in the impulse circuit will occur before the previously excited trains of oscillations in the oscillatory circuit die down, said oscillations in the oscillatory circuit reacting on the impulse circuit and serving to trigger off the condenser discharges in a predetermined phase relation With the oscillations so as to reinforce and sustain the declining oscillations.

9. Apparatus for producing electrical oscillations having, in combination, an oscillatory circuit, an impulse circuit closely coupled With the oscillatory circuit and including a condenser and a sectored rotary discharge gap, a feeder circuit forcharging the condenser at such a rate that a number of condenser discharges occur upon each coincidence of the gap sectors, and a reservoir circuit shunted across the condenser and including inductance and capacity so proportioned that the reservoir circuit'has approximately the same natural frequency as the frequency of coincidence of the sectors of the gap.

10. Apparatus for producing electrical oscillations having, in combination, an oscillatory circuit, an impulse circuit closely coupled with the oscillatory circuit and including a condenser and a discharge gap having provision for dividing the condenser discharges into groups having an audible I group frequency, a feeder circuit for charging the condenser, and a reservoir circuit shunted around the condenser lncluding capacity and inductance so proportioned that the reservoir circuit has a natural frequency 3 approximately that of the group frequency.

11. Apparatus for producing electrical oscillations having, in combination, a circuit including a condenser and a discharge gap having provision for dividing the condenser discharges into groups of audible frequency, a feeder circuit for charging the condenser, and a reservoir circuit shunted around the condenser including inductance and capacity so proportioned that it has a natural frequency approximately that of the group frequency.

MELVILLE EASTHAM. 

